LEDs (and in particular GaN LEDs) have proven useful for a variety of lighting applications (e.g., full-color displays, traffic lights, etc.), and have potential for even more applications (e.g., backlighting LCD panels, solid state lighting to replace conventional incandescent lamps and fluorescent lights, etc.) if these LEDs can be made more efficient and can also be manufactured more cost-effectively. To realize higher efficiency for GaN LEDs, they need to have enhanced output power, lower turn-on voltage and reduced series resistance. The series resistance in GaN LEDs is closely related to the efficiency of dopant activation, uniformity of current spreading, and ohmic contact formation. To realize manufacturing cost-effectiveness, improvements in the manufacturing process that result in better processing uniformity and a reduction on adverse processing effects is desirable.
In GaN, a n-type dopant can be readily achieved using Si and with an activation concentration as high as 1×1021 cm−3. The p-type GaN can be obtained by using Mg as the dopant. The efficiency of Mg doping, however, is quite low due to its high thermal activation energy. At room temperature, only a few percent of the incorporated Mg contributes to the free-hole concentration. Mg doping is further complicated during MOCVD growth because of hydrogen passivation during the growth process. Hydrogen passivation requires a thermal annealing step to break the Mg—H bonds and activate the dopant.
A GaN LED typically includes conductive contacts and conductive current-spreading electrodes to power the LED. However, the resulting pattern can interfere with the laser annealing process and give rise to so-called adverse “pattern effects.” To improve the performance of a GaN LED, it would be desirable to perform laser annealing of the LED structure after the current spreading electrodes are formed. Consequently, there is a need for systems and methods of performing laser annealing that reduces adverse pattern effects when laser annealing through conductive structures.